The present invention relates to a roller drive unit for use in the transportation of freight containers and the like.
Roller drive units of this type are disposed, for example, in a roller conveyor track for the transportation of items of cargo, which usually comprise freight containers or freight pallets. In particular, a roller drive unit as proposed in the present invention is preferably of the type for installation in the cargo hold of a freight-transporting aircraft in such a way that a plurality of them form roller conveyor tracks by means of which containers, or the cargo to be conveyed is transported over rollers into the cargo hold and stored in the place provided.
When such a roller drive unit is turned on, an associated roller is swiveled upward so as to press against the bottom of a freight container situated above it. Owing to the resulting frictional engagement, the torque of the drive roller is transferred to the bottom of the freight container and the latter is thereby moved.
In the roller drive unit disclosed in the European Patent EP 0 391 175 A2, the item of cargo can only be moved forward or backward. Roller conveyor tracks formed of such roller drive units allow cargo items to move only in a direction determined by the orientation of the drive rollers of the roller drive unit or in the reverse direction. In order to store the cargo item suitably in the cargo space, therefore, as a rule it is necessary for the operating staff to push the item manually from one roller conveyor track to the next roller conveyor track until the item comes into the region of the intended storage place. Once it is in this region, the cargo item must, again manually, be moved into the intended place. As a result, the loading and unloading process is quite lengthy and hence also expensive, in particular because the airport fee depends on the time the aircraft spends in the airport.
Considering this background, it is desirable to make available a roller drive unit, or roller conveyor tracks constructed of such units, that can convey items or cargo to virtually any desired place within a cargo hold without significant manual shifting by the operating staff being required.
The difficulties in constructing such a roller drive unit lie on one hand in the need to make the force with which the drive roller presses against the bottom of the container as strong as possible, while on the other hand to make possible the changing of the conveying direction of the roller drive unit, both when the drive roller of the roller drive unit is retracted and when it is raised. Furthermore, the drive roller must be capable of being swiveled upwards when its drive motor is switched on and downwards when the motor is switched off, regardless of the direction in which the container is to be moved. Despite these various, mechanically difficult requirements, the drive unit must be of small dimensions and of low weight, both indispensable prerequisites for its main intended use in aircraft. Because a plurality of such roller drive units are employed simultaneously in a conveyor track, their reliability must be particularly high. The failure of even a single roller drive unit can disrupt the loading process.
The object of the invention is therefore to provide a reliable and nevertheless light-weight roller drive unit that is capable of conveying containers in any desired direction.
According to the present invention there is provided a roller drive unit for the transportation of freight containers in a plurality of directions comprising a substantially annular fixing means for attachment of the roller drive unit to a floor of a cargo hold; a drive roller for rotational engagement with a freight container to be transported; and a carrier means for the drive roller and relative to which the drive roller can be retracted and can be raised into an operating position for rotational engagement with said freight container, the carrier means being located within the annular fixing means and being rotatable relative thereto in a direction perpendicular to the notional plane of the floor.
It is important that the actuation of the drive roller, that is its raising and rotation as well as its rotation relative to the fixing means by the carrier means, is achieved with the smallest possible number of driving means such as electric motors. Preferably, therefore, a transmission system, such as a planetary gear system, is provided having a first output driving shaft which is used to raise the drive roller in order to produce a frictional engagement with the freight container and having a second output driving shaft which is used to rotate the carrier means relative to the fixing means about a vertical axis, advantageously as predetermined by an automatic or manual control apparatus.
In a planetary gear system, the first output driving shaft is preferably the shaft of a planet wheel carrier of the system, and the second output shaft is preferably a ring gear or hollow shaft of the system. Depending on the disposition of the planetary gear system in the roller drive unit, the carrier means for the drive roller can also be driven by the hollow shaft of the planetary gear system. The drive shaft of the gear system is then preferably the shaft of the sun wheel, which is driven by a first electric motor. The first electric motor and/or the planetary gear is preferably disposed in a suitable manner within the rotatable carrier means element and during rotation actuates a pinion that meshes with a toothed rim on the carrier means.
In a roller drive unit comprising such a planetary gear system, advantageously only two motors are needed to produce rotation of the drive roller, raise it and press it against a freight container to be transported, and to rotate the drive roller into a desired direction as predetermined by the control apparatus.
Preferably, in the region of the first and the second output driving shafts of the planetary gear, at least one separately actuatable output braking mechanism is provided which operates to brake the driving action of at least one of the first and the second output driving shafts when required. Advantageously, there is provided one braking mechanism for each shaft, the two mechanism being separately electrically actuatable. By this means a driving action of the first and/or the second output shaft, when not needed, can be stopped more or less gradually by braking the output shaft.
Preferably, a second electric motor is provided to rotatably drive the drive roller.
Preferably also, a variable gear means is connected between the drive roller and the second electric motor.
Similarly, an actuatable braking mechanism is preferably provided for immobilization of the drive roller.
A sensing means is preferably also provided to measure the velocity of a freight container being transported by the drive roller.
Alternatively or in addition, the drive roller can be provided, preferably at one of its end faces, with a toothed wheel or a pinion and/or have a toothed outer or inner surface. Then in addition there is preferably provided a holder means which is rotatably mounted to one side of the carrier means for rotational movement upwards and downwards and to which the drive roller is rotatably mounted, the second electric motor being provided to drive the drive roller via the variable gear means.
A first measuring means for measuring the rotational speed of the drive roller and a second measuring means for measuring the force with which the drive roller engages a surface of the freight container to be transported when the drive roller is in a raised operating position can be provided in a preferred embodiment of the invention.
Various aspects of the present invention will now be described by way of example with reference to the accompanying drawings.